Drainage aid for metal heap leaching

ABSTRACT

Methods for increasing drainage or percolation of a lixiviant solution through mineral ore in a heap mining operation. A drainage aid comprising ethoxylated aliphatic primary alcohols and mixtures thereof is dripped, sprayed or otherwise brought into contact with the heaped metal ore aggregate and thereby improves percolation or drainage of the lixiviant through the heaped metal ore.

FIELD OF THE INVENTION

[0001] The present application relates to an improved process forleaching of metal from ore heaps in which a lixiviant solution isbrought into contact with the ore to form a “pregnant” solution, fromwhich the metal is ultimately separated. The improvement lies incontacting the metal ore with an ethoxylated aliphatic alcohol toimprove percolation of the lixiviant through the heap.

BACKGROUND OF THE INVENTION

[0002] In recent years, heap leaching has become a cost effective methodfor recovering precious metals such as gold or silver from low gradeores. In the process, a lixiviant system, comprising a ligant and anoxidant is used to dissolve out the desired precious metal from the ore.As used herein, the phrases “lixiviant system” and “lixiviant solution”will be used interchangeably and do not imply a true chemicalsolution—only a chemical combination adapted to extract the mineralvalue in the ore.

[0003] In heap leaching, the metal bearing ore may be obtained from anopen pit mine or the like and is crushed to produce an aggregate that iscoarse enough to expose the desired mineral values but fine enough toallow intimate contact of the lixiviant system or solution therewith.The lixiviant solution may be distributed over the top of the metal oreheap via sprinklers, wobblers, or other similar equipment. The barrenlixiviant “percolates” through the heap to perform its desired functionwith the metal and the resulting pregnant solution is then collected byan impervious leach pad or the like located at the bottom of the heap.The pregnant solution is then subjected to conventional mineral recoverytechniques to obtain the desired precious metal.

[0004] In gold heap mining operations, a lixiviant system comprisingcyanide, air and lime is commonly used under highly alkaline conditions(pH 9-11.5) to form the pregnant solution, (i.e., a complex or ligandcoordinated with a gold cation). The gold cation complex or ligandleaches from the ore heap and is recovered. The gold is then separatedfrom the lixiviant complex via conventional separation techniques suchas the conventional method of adsorption on an activated carbon columnor bed.

[0005] A variety of factors can contribute to poor percolation of thelixiviant through the heap. For example, high clay ores, the formationof large rock fragments and the formation of surface muds or slimes onthe heap can be detrimental to the desired percolation through andcontact of the ore with the lixiviant solution.

[0006] It is therefore desirable to provide a treatment that can enhancethe percolation or contact of the ore with lixiviant solution so as toincrease the amount of precious metal recovered per unit area of themetal ore heap.

[0007] It is especially desirable to provide such a percolation ordrainage aid that does not severely impede the functioning of desiredprocess parameters such as the ability of the lixiviant solution toreact or complex with the ore, or the ability of the pregnant lixiviantsolution to drain through the heap for recovery.

SUMMARY OF THE INVENTION

[0008] The present invention is directed to a drainage aid useful inheap mining operations. More preferably, the invention is directedtoward precious metal heap leaching operations such as gold heapleaching. The drainage aid can be applied by itself to the heap or itcan be mixed with the lixiviant solution and then sprayed or drippedonto the ore to thereby contact the ore.

[0009] The drainage aid is preferably applied in an aqueous solution viadrip or spray application and is present in the aqueous solution in anamount of between about 1-1,000 ppm. The drainage aid is an ethoxylatedaliphatic primary alcohol having a carbon chain length of from aboutC₄-C₂₀ and about 2-20 moles of ethoxylation per molecule.

[0010] The invention will be further described in the following detaileddescription and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a graph showing the results of activated carbon golduptake tests reported in Example 4; and

[0012]FIG. 2 is a bar graph illustrating the tests reported in Example 5showing the uptake of the drainage aids by gold ore.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0013] The drainage aids in accordance with the invention areethoxylated aliphatic alcohols having the formula

HOCH₂CH₂—O_(n)R

[0014] wherein R is C₄-C₂₀ alkyl or C₄-C₂₀ alkenyl with n being about 2to 20. More preferably, R is C₄-C₁₄ alkyl or C₄-C₁₄ alkenyl and n isabout 3 to 8.

[0015] Preferably, the drainage aid is applied to the metal ore in theform of an aqueous solution with the drainage aid present in an amountof about 1-1,000 preferred, about 1-500 ppm active more preferred, and1-100 ppm most preferred.

[0016] The ethoxylated aliphatic alcohols are commercially availablefrom a plurality of suppliers. Based upon presently available data, thefollowing four commercially available products appear to be especiallyeffective. McCutcheon Description description Analysis resultsEthoxylated Isodecyl alcohol A heavily branched ethoxylated aliphaticethoxylate aliphatic alcohol. The average carbon alcohol chain length is7.3 C's/molecule. The average ethoxylation is 4.5 moles/ moleculeEthoxylated 2-decylethoxy a heavily branched ethoxylated aliphaticaliphatic poly(ethyleneoxy) alcohol. The average carbon chain alcoholethanol length is 6.7 C's/molecule. The average ethoxylation is 5.3moles/molecule Ethoxylated Ethoxylated a heavily branched alcohol 1aliphatic 2-decanol ethoxylated aliphatic alcohol. The alcohol averagecarbon chain length is 10.5 C's molecule. The ethoxylation is 3.5moles/molecule Ethoxylated Ethoxylated a straight chain ethoxylatedaliphatic aliphatic alcohol alcohol. The average carbon chain alcohollength is 12.2 C's/molecule. The average ethoxylation is 4.0 moles/molecule

[0017] At present, the most preferred treatment is the 2-decylethoxypoly (ethyleneoxy) ethanol.

EXAMPLES

[0018] The invention will be further explained in conjunction with thefollowing illustrative examples which should not be construed as alimitation on the inventive concepts set forth herein

[0019] A drainage aids for heap leaching must have certain desirablecharacteristics and not have some undesirable characteristics. Fivetests proving these characteristics have been developed to determine thesuitability of potential drainage aids for gold heap leach applications.The importance of the ability of a potential drainage aid to pass eachtest is described below.

[0020] capillary rise in gold ore—the basic desired outcome forapplication of a drainage aid is that it reduce the extent of capillaryrise in a gold ore. Reduction of capillary rise especially in smallerore particles is important to promote uniform movement of lixiviantthrough the heap. Excessive capillary rise will lead to so-called“blinding” so that movement of cyanide and oxygen into and gold cyanidecomplex out of that portion of the heap is greatly reduced. A successfuldrainage aid will have the maximum possible reduction in capillary riseat a given concentration.

[0021] goldfilm dissolution inhibition—While it is important that adrainage aid reduce heap blinding, it is equally important that thedrainage aid not impede gold dissolution from the ore. Gold is generallypresent in ore as particles of metallic gold in the rock matrix. Anycoating of the gold metal by the drainage aid could slow the dissolutionprocess leading to slower recovery of the gold value, an undesirableoutcome. The use of a surface-active agent to modify capillary risecould reasonably be expected to have an impact on gold dissolution asany surface film formed by the surfactant could interfere with the golddissolution reaction. Given equal drainage properties, the drainage aidwith the least effect on gold dissolution would be the most successful.

[0022] clear solution cyanide reactivity—Another important property thata potential drainage aid must possess is an inertness to cyanide underleaching conditions (pH9-11.5, 7-9 ppm oxygen). Cyanide concentration isone of the two important parameters (the other is oxygen concentration)which affect gold dissolution rates. A drainage aid that reacts withcyanide to reduce cyanide concentration in the heap will also lead to aslower recovery of the gold value. Given equal drainage properties, thedrainage aid with the least effect on cyanide concentrations would bethe most successful.

[0023] activated carbon gold uptake—After gold is leached from a heap,it is passed through a column of activated carbon to strip the goldcyanide from the lixiviant (so-called carbon-in-column (CIC) goldrecovery). Any drainage aid which prevents the uptake of gold by theactivated carbon would not be desired unless it could be shown that inactual practice the drainage aid does not reach the activated carboncolumn. Again as surface-active agents are being used, it is areasonable expectation that gold uptake would be affected by thefilm-forming properties of the agent on the activated carbon.

[0024] uptake of the drainage aid by gold ore—If the drainage aid had adetrimental effect on activated carbon gold uptake, it is still possiblethat a drainage aid could be successfully applied if it were adsorbedonto the ore in the process of improving drainage. As is stated in U.S.Pat. No. 5,827,348, proper wetting of the ore is an important factor inoptimizing precious metal recovery.

[0025] A large number of potential drainage aids were initially testedusing a capillary rise experiment to determine if they had any effect ondrainage. Potential drainage aids were selected on the basis of theirstability in high pH (pH 10.5) solutions and a stated ability (inMcCutheon's Emulsifiers and Detergents 1999: North American Edition,Vol. 1) to impact wetting. Those tested included fatty acid derivatives(such as those described in AU application 07/011,659), ethyleneoxide/propylene oxide block copolymers (such as those described by Smithand Craft in Chapter 5 of Heap and Dump Leaching Practice),sulfosuccinate derivates (such as those described in U.S. Pat. No.5,827,348), ethoxylated alkylphenols, betaine derivatives, variousphosphate esters, caprylic and imidazoline amphoterics, sulfonatedaromatics, silicones, 2-ethyl hexyl sulfate, various ethoxylatedaromatic alcohols, branced- and straight-chain aliphatic alcohols, andsome proprietary mixtures of surfactants provided by manufacturers.

Example 1

[0026] Benchtop Capillary Rise Experiments.

[0027] Capillary rise screening tests were performed using an 18×30 meshsieved ore from a mine in Northern Nevada (Marigold Mine). The ore wasprepared by first sieving to this size fraction. The 18×30 fraction waswashed extensively with tap water to remove embedded clays. Material wasdried overnight at 105° C. and then stored in an environmental chamberat 50% humidity and 25 C.

[0028] A 1 cm×30 cm plastic tube was prepared with a fine stainlesssteel mesh pushed to the bottom of the tube to hold the ore in place.The tube was filled about ⅔ full with the sieved, washed, and dried oreand suspended from the bottom weighing hook of a Mettler analyticalbalance. A petri dish was filled with a solution of the surfactant atthe desired concentration prepared in buffer solution. The buffersolution was prepared by dissolving 0.1 gram of calcium oxide per literof solution along with 400 ppm of sodium sulfate (expressed as sulfate)adjusted to a pH of 10.5 with sulfuric acid. The sulfate was added tomore closely approximate the high ionic strength of a typical lixiviantsolution. Some surfactants show reduced activity at his ionic strength,therefore it was important that test solutions match a typicallixiviant.

[0029] The petri dish was placed under the suspended plastic tube andraised with a lab jack until the solution just touched the bottom of thetube and solution began to rise in the tube due to capillary action.Capillary rise was monitored by the rise in the liquid level in the tube(easily see as a darkening of the tube interior) and by the weight gainof the tube.

[0030] The liquid was allowed to enter the tube for seven minutes afterwhich the petri dish was lowered, the gain in weight of the tube wasmeasured and then the tube was removed from the hook to measure theheight. In general, weight gain and the rise of liquid were highlycorrelated for a given ore so that the two measurements were used aschecks on each other. Height of the wetted column after seven minutes isreported below.

[0031] Surfactants were run at 5, 20 and 100 ppm. Below the surfactantsare described as one of three classes, those that no effect or doesresponse (>95% of blank, approximate noise level of experiment), thosethat slightly decreased capillary rise with increasing dose (75% to95%), and those that had a significant impact (<75% of blank). heightheight % Classifi- Type chemical name cm of blank cation EthoxylatedEthoxylated 6.8 66% Good effect aliphatic alcohol 2-decanol Proprietary7.0 68% Good effect fatty acid + sodium laureth(2) 7.0 68% Good effectamphoteric sulfate Ethoxylated isodecyl alcohol 7.0 68% Good effectaliphatic alcohol ethoxylate Ethoxylated Ethoxylated 7.1 69% Good effectaliphatic alcohol alcohol sulfonate aliphatic sodium dioctyl- 7.3 71%Good effect sulfosuccinate fatty acid + ammonium lauryl 7.3 71% Goodeffect amphoteric sulfate/ ammonium laureth sulfate/ cocoamidopropylbetaine/ cocamide dea fatty acid + sodium laureth(3) 7.5 73% Good effectamphoteric sulfate fatty acid + ammonium 7.5 73% Good effect amphotericlaureth(3) sulfate mixed fatty acid sulfo 7.6 74% Good effect saltEthoxylated Ethoxylated 7.7 75% Good effect aliphatic alcohol 2-decanolSulfonate sodium dodecyl 7.8 76% Some effect aromatic diphenyloxidedisulfonate sulfonate aliphatic dihexyl sodium 7.9 77% Some effectsulfosuccinate Ethoxylated Alkoxylated 8.2 80% Some effect aliphaticalcohol isopropanolamide acrylic acid 8.7 85% Some effect ProprietaryModified 8.7 85% Some effect ethoxylate sulfonate aliphatic tetrasodium8.7 85% Some effect N-(1,2 dicarboxyethyl)- octadecyl sulfosuccinatefatty acit + sodium laureth(1) 8.8 86% Some effect amphoteric sulfatefatty acid ammonium lauryl 8.8 86% Some effect sulfate EthoxylatedLauryl alcohol 9.0 88% Some effect aliphatic alcohol alkoxylatesulfonate aliphatic di-tridecyl sodium 9.2 90% Some effectsulfosuccinate sulfonate sodium di- 9.2 90% Some effect aromaticisopropyl naphalene sulfonate Proprietary 9.3 91% Some effectEthoxylated C-12 to C-14 9.5 93% Some effect aliphatic alcohol secondaryalcohol ethoxylate Ethoxylated ethoxylated 9.5 93% Some effect aromaticalcohol nonylphenol Ethoxylated C-12 to C-14 9.6 94% Some effectalphatic alcohol secondary alcohol ethoxylate phosphate ester aromaticbased 9.7 95% No effect organic phosphate ester sulfonate aliphaticdibutyl sodium 9.7 95% No effect sulfosuccinate Silicone Silicone glycol9.7 95% No effect copolymers Ethoxylated ethoxylated 9.8 96% No effectaromatic alcohol nonylphenol Proprietary 9.9 97% No effect Proprietary9.9 97% No effect block copolymer EO/PO 10.0 98% No effect copolymeramphoteric Alkylether 10.0 98% No effect betaine hydroxysultaineEthoxylated C-12 to C-14 10.0 98% No effect aliphatic alcohol secondaryalcohol ethoxylate amphoteric caprylic 10.1 99% No effect caprylicamphoteric amphoteric imidazoline 10.1 99% No effect imidazoline sodiumsalt sulfonate aliphatic disodium alkoxy 10.1 99% No effectsulfosuccinate amphoteric sodium salt of 10.2 100%  No effectimidazoline 2-caprylic-1 (ethyl beta oxypropanoic acid) amphotericcocoamidopropyl 10.3 100%  No effect betaine block copolymer EO/PO 10.4101%  No effect copolymer amphoteric cocoamidopropyl 10.4 101%  Noeffect betaine sulfobetaine sulfate 2-ethyl hexyl 10.6 103%  No effectsulfate Proprietary 10.7 104%  No effect Ethoxylated Ethoxylated 10.9106%  No effect aromatic alcohol alkylphenol

[0032] Of the surfactants showing a maximum reduction in capillary rise(“good effect”), it was found that these were of four types, asulfosuccinate, ethoxylated aliphatic alcohols, mixtures of fatty acidsand amphoterics, and a sulfo salt of a fatty acid. A fifth material isdescribed by its manufacturer as a mixture of anionic and nonionicsurfactants. The fatty acid/1 mixtures were found to be too expensiveand were not tested further.

[0033] It is interesting to note that the longer chain ethoxylatedaliphatic secondary alcohols did not show any effect; neither did theethoxylated aromatic alcohols. With regard to the sulfosuccinates, onlysodium dioctyl-sulfosuccinate and possibly dihexyl sodium sulfosuccinateshowed an appreciable impact on capillary rise.

Example 2

[0034] Goldfilm Dissolution Inhibition

[0035] Gold dissolution rates were monitored in the presence and absenceof the candidate drainage aids. The technique used was similar to thatdescribed in U.S. Pat. No. 5,484,470. Gold metal films sputtered onto ¼″cm×2″ plastic film backings were prepared. The gold film was strippedfrom the film in the presence of cyanide at pH 10.5 in a magneticallystirred UV-Vis cuvette. Gold dissolution was monitored during thestripping using a Au(CN)⁻ ₂ absorption peak at 240 nm. The absorbance atthis wavelength is linearly related to Au(CN)⁻ ₂ for concentrations upto 20 ppm.

[0036] The experiment was run for 15 minutes. Initially, no surfactantwas added to the cuvette. After 1 minute, monitoring of the rise in theAU(CN)⁻ ₂ absorbance peak began at one minute intervals until 6 minutes.At 7 minutes, 100 ppm of surfactant was added to the solution using amicroliter pipette. Monitoring the Au(CN)⁻ ₂ continued until 15 minutes.The slope of the increase in absorbance taken from 7 to 10 minutes wasexpressed as a percentage of the slope for 1 to 6 minutes. Typically,the slope for a blank (no surfactant solution) was slightly (10%) lowerthan that at the start of the experiment. A suppression of the golddissolution by a surfactant was seen as a further decrease in the ratio(or percentage) of the slopes after and before surfactant addition.

[0037] Examples of the four top classes of surfactants from thecapillary rise experiments were compared to blank (no surfactant)solution. The materials included ethoxylated 2-decanol, fatty acid sulfosalt; LD-450 (Stephan-Proprietary); and sodium dioctyl sulfosuccinate.Because of claims made in U.S. Pat. No. 4,929,274 about thehydrolyzability of the sodium dioctyl sulfosuccinate, tests were doneusing both hydrolyzed (prepared by allowing an alkaline solution to sitovernight) and unhydrolyzed (freshly prepared) solutions. The resultsare shown in the table below: C-3 C-4 Blank X-1 C-1 C-2 (fresh) (aged)Average % of slopes 89% 81%  9%  9% 45% 44% (8 to 15 minutes)/ (1 to 6minutes) Standard deviation of 11%  5% 20% 21% of ave % % decrease indissolution  0%  9% 90% 90% 50% 51% rate from blank {Ave %_(sample) −Ave %_(blank)}/Ave %_(blank)

[0038] Of the tested materials only X-1 showed acceptable performance.Both C-1 and C-2 had a dramatic inhibitory effect on dissolution,reducing the dissolution rate by 90% compared to the blanks. C-3 reducedthe gold dissolution by about 50%. Aged (hydrolyzed) C-4 had the sameeffect as fresh C-3. X-1 had no statistically significant impact on thegold dissolution rate.

[0039] X-1=ethoxylated 2-decanol

[0040] C-1=LD450—Stepan-proprietary

[0041] C-2=fatty acid sulfo salt

[0042] C-3=sodium dioctyl sulfosuccinate

[0043] C-4=hydrolyzed sodium dioctyl sulfosuccinate

Example 3

[0044] Clear Solution Cyanide Reactivity

[0045] Experiments were completed evaluating the effect of the same foursurfactants on cyanide consumption after 1 and 24 hours. Testing wasconducted at 50 and 100 ppm of these surfactants (as actives) in thepresence of 25 ppm cyanide (much higher surfactant/cyanide ratios thanexpected in an actual application). The experiments were done in stocksolutions of 1 g/L Ca with 400 ppm of sulfate added, adjusted to pH10.5.

[0046] Analysis of free CN was done using a LACHAT Flow InjectionAnalyzer and an analysis method which converts CN in an alkaline mediato cyanogen chloride, CNCl, by reaction with chloramine-T at pH<8. TheCNCl then forms a red-blue dye by reacting with a pyridine-barbituricacid reagent. The resulting color is read at 570 nm. The results areshown below: Exposure time, hrs 1 24 surfactant concentration, ppm 50100 50 100 C-3 96% 96% 95% 96% C-1 100%  96% 96% 98% C-2 96% 96% 95% 96%X-1 98% 94% 96% 91%

[0047] Within the error of the cyanide analysis methodology (±10%), noneof the surfactants had a negative effect on cyanide consumption.

Example 4

[0048] Activated Carbon Gold Uptake

[0049] Similar types of experiments have been reported in U.S. Pat. No.5,827,348.

[0050] Stock solutions of gold cyanide were prepared by dissolving 0.900g of KAu(CN)₂ and 12.6 g. of NaCN (95%) in DI water to 55 liters. Thesolution pH was adjusted to pH 10.5. After gold analysis, the stocksolutions were diluted further with DI water to adjust the goldconcentration to 10.25 mL. This gives a test solution concentration of10 ppm and approximately 200 ppm NaCN. Stock solutions of the reagentswere prepared to contain 2000 ppm of active surfactant in a 500 mLsolution. The pH was adjusted to pH 10.5 with lime before finaldilution. Surfactants prepared using this procedure included C-3, X-2,C-5, C-1, X-3, X-1, C-6, C-2, X-4, C-7, C-8.

[0051] For a test, the specified volume of 10.25 ppm gold stock solutionis placed in a 2.5 liter bottle along with the required amount ofsurfactant stock solution to obtain the desired surfactant concentration(0 ppm, 10 ppm, 50 ppm). Additional DI water was added to adjust thegold concentration to 10 ppm. The required amount of preattrited (+20mesh) Calgon GRC-22 carbon was added. For each surfactant concentration,five solution to carbon ratios were tested as shown in the table below.The ratio of gold solution volume to weight of carbon (“carbon loading”)is an important factor in representing what might happen in a carbonstripping column. As gold is progressively loaded onto a carbon column,a profile of loading values is created across the column. It isimportant to know if an inhibitor of the gold adsorption process affectsthe process at both low and high solution to carbon ratios. Gold ReagentTotal Solution Stock Test Solution to Sol. Carbon Conc. Volume CarbonTest mL g mg/L mL Ratio 1 1500 0.3 10 1538 5125 2 1000 0.4 10 1025 25633 500 0.4 10 513 1281 4 500 0.8 10 513 641 5 450 1.5 10 461 308

[0052] Each bottle was rolled for 48 hours then a sample of the solutionwas filtered and analyzed for gold expressed as ppm of gold in solution.The carbon with loaded gold was fire-assayed for its gold contentexpressed as kilograms of gold per metric ton of carbon. A plot ofresults (carbon loading vs. solution gold concentration) is shown inFIG. 1.

[0053] Reference numerals used in FIG. 1 are as follows:

[0054]20—control

[0055]22—C-8; di-tridecyl sodium sulfosuccinate

[0056]24—C-6; dihexyl sodium sulfosuccinate

[0057]26—C-2; fatty acid sulfo salt

[0058]28—C-3; sodium dioctyl sulfosuccinate

[0059]30—C-1; LD 450 Stepan proprietary

[0060]32—C-5; ammonium lauryl sulfate/ammonium laureth sulfate/cocoamidopropyl betaine/cocamide dea

[0061]34—X-1; ethoxylated 2-decanol

[0062]36—X-3; isodecyl alcohol ethoxylate

[0063] The results clearly show that all surfactants (with the possibleexception of C-8, di-tridecyl sodium sulfosuccinate) have a detrimentaleffect on carbon loading at 50 ppm. Running the same experiments at 10ppm show a decreased but still significant impact of surfactant onrecovery.

Example 5

[0064] Uptake of the Drainage Paid by Gold Ore

[0065] As mentioned above, if the drainage aid had a detrimental effecton activated carbon gold uptake, it is still possible that a drainageaid could be successfully applied if it were adsorbed onto the ore inthe process of improving drainage. Tests were conducted with the fourmost cost-effective drainage aids to determine their retention on arepresentative oxide gold ore from Northern Nevada.

[0066] As with the capillary rise experiments, the uptake experimentswere done using an 18×30 mesh sieved ore. The ore was prepared by firstsieving to this size fraction. The 18×30 fraction was washed extensivelywith tap water to remove any embedded clays. Material was driedovernight at 105° C. and then stored in environmental chamber at 50%humidity and 25 C.

[0067] A 1 cm×30 cm plastic tube was prepared with a fine stainlesssteel mesh pushed to the bottom of the tube to hold the ore in place.Ore was filed to a height of 10 cm in the tube and 10 ppm surfactantsolutions were dripped onto the ore at a pumping rate (3.24 ml/min)corresponding to a typical heap leach application rate of 0.005 gpm/ft².Buffer solution was the same as the capillary rise experiments, 0.1 gLCa with 400 ppm sulfate added, adjusted to pH 10.5 with sulfuric acid.

[0068] The experiments were run over 66 hours during which a compositesample of the effluent solution was collected.

[0069] Uptake of surfactant by the ore was measured using total carbonafter acidification with a Shimadzu Model TOC-5000 Carbon Analyzercalibrated using potassium hydrogen pthalate standards. Recovery wascalculated by the following equation:

(Effluent Total Carbons_(surfactant)−Influent TotalCarbon)_(surfactant)−(Effluent Total Carbon_(blank)−Influent TotalCarbon)_(blank)

[0070] Results are shown in the graph shown in FIG. 2.

[0071] Reference numerals used in FIG. 2 are as follows: 2 C-3 4 X-22-decylethoxy Poly (ethyleneoxy) ethanol 6 C-5 8 C-1 10 X-1 12 C-6 14C-2 16 X-4 ethoxylated alcohol 18 C-7 sodium dodecyl diphenyl oxidedisulfonate

[0072] Combining the results of all five of the above examples, oneclass of compounds successfully meets the desired criteria for a goldheap leach application. Specific commercial products of this class (CAS# 61827-42-7) which demonstrated efficacy include the following:McCutcheon Description description Analysis results Ethoxylated Isodecylalcohol A heavily branched ethoxylated aliphatic ethoxylate aliphaticalcohol. The average carbon alcohol chain length is 7.3 C's/molecule.The average ethoxylation is 4.5 moles/ molecule (X-3) Ethoxylated2-decylethoxy a heavily branched ethoxylated aliphatic aliphaticpoly(ethyleneoxy) alcohol. The average carbon chain alcohol ethanollength is 6.7 C's/molecule. The average ethoxylation is 5.3moles/molecule (X-1) Ethoxylated Ethoxylated a heavily branched alcoholethoxylated aliphatic 2-decanol aliphatic alcohol. The average carbonalcohol chain length is 10.5 C's molecule. The ethoxylation is 3.5moles/molecule (X-2) Ethoxylated Ethoxylated a straight chainethoxylated alcohol aliphatic alcohol aliphatic alcohol. The averagecarbon alcohol chain length is 12.2 C's/molecule. The averageethoxylation is 4.0 moles/ molecule (X-4)

[0073] The invention is therefore applicable to enhance drainage orpercolation of lixiviant solutions such as the cyanide based lixiviantsolutions through a heap of mineral ore. The invention performsparticularly well in the leaching of gold from gold ore with acyanide/oxygen/lime lixiviation system operated at a pH of from about9-11.5 but is also applicable to other heap mining environments such asprecious metal heap mining in general and copper heap mining.

[0074] While the present invention has been described with respect toparticular embodiments thereof, it is apparent that other forms andmodifications of the invention will be obvious to those skilled in theart. The appended claims and this invention generally should beconstrued to cover all such obvious forms and modifications which arewithin the true spirit and scope of the present invention.

What is claimed is:
 1. In a method of leaching metals from metal ore inwhich a lixiviant solution is placed in contact with said metal ore toextract said metal therefrom, the improvement comprising contacting saidmetal ore with an effective amount of a drainage aid comprising anethoxylated aliphatic alcohol.
 2. Method as recited in claim 1 whereinsaid ethoxylated aliphatic alcohol has the formula HOCH₂CH₂—O_(n)Rwherein R is C₄-C₂₀ alkyl or C₄-C₂₀ alkenyl and n is from about 2 toabout
 20. 3. Method as recited in claim 2 wherein R is C₄-C₁₄ alkyl orC₄-C₁₄ alkenyl and n is about 3 to about
 8. 4. Method of recited inclaim 2 wherein said step of contacting said metal ore comprisescontacting said metal ore with an aqueous solution containing saiddrainage aid, said drainage aid being present in said aqueous solutionin an amount of about 1-1,000 ppm.
 5. Method as recited in claim 4wherein said drainage aid is present in an amount of about 1-500 ppm. 6.Method as recited in claim 4 wherein said drainage aid is present in anamount of about 1-100 ppm.
 7. Method as recited in claim 3 wherein saiddrainage aid comprises a mixture of ethoxylated aliphatic alcohols andwherein, in said mixture, R is about 7.3 alkyl and n is about 4.5. 8.Method as recited in claim 3 wherein said drainage aid comprises amixture of ethoxylated aliphatic alcohols and wherein, in said mixture,R is about 6.7 alkyl and n is about 5.3.
 9. Method as recited in claim 3wherein said drainage aid comprises a mixture of ethoxylated aliphaticalcohols and wherein, in said mixture, R is about 10.5 alkyl and n isabout 3.5.
 10. Method as recited in claim 3 wherein said drainage aidcomprises a mixture of ethoxylated aliphatic alcohols and wherein, insaid mixture, R is about 12.2 alkyl or alkenyl and n is about
 4. 11. Ina method of leaching gold from a heap of gold metal ore in a heapleaching operation wherein a cyanide based lixiviant system is used tocontact and remove gold from said gold metal ore, the improvementcomprising contacting said gold metal ore with a drainage aid comprisingan ethoxylated aliphatic alcohol or mixtures of said ethoxylatedaliphatic alcohol.
 12. Method as recited in claim 11 wherein saidlixiviant system has a pH of about 9 to about 11.5 and wherein saidethoxylated aliphatic alcohol is a primary alcohol having a carbon chainlength of about 4 to about 20 carbon atoms and average ethoxylation ofabout 2-20 moles of EtO (ethylene oxide) per molecule.
 13. Method asrecited in claim 12 wherein said ethoxylated aliphatic primary alcoholis present in an aqueous solution in an amount of about 1—about 1,000ppm.
 14. Method as recited in claim 13 wherein said ethoxylatedaliphatic primary alcohol is present in an amount of about 1-500 ppm.15. Method as recited in claim 13 wherein said ethoxylated aliphaticprimary alcohol is present in an amount of about 1-100 ppm.
 16. Methodas recited in claim 12 wherein said carbon chain length is from about4-14 and said average ethoxylation is about 3 to about 8 moles of EtOper molecule.
 17. Method as recited in claim 13 wherein said drainageaid comprises a mixture of ethoxylated aliphatic primary alcohols. 18.Method as recited in claim 17 wherein said mixture has an average carbonchain length of about 7.3 and an average of about 4.5 moles of EtO permolecule.
 19. Method as recited in claim 17 wherein said mixture has anaverage carbon chain length of about 6.7 and an average of about 5.3moles of EtO per molecule.
 20. Method as recited in claim 17 whereinsaid mixture has an average carbon chain length of about 10.5 and anaverage of about 3.5 moles of EtO per molecule.
 21. Method as recited inclaim 17 wherein said mixture has an average carbon chain length ofabout 12.2 and an average of about 4 moles of EtO per molecule. 22.Method as recited in claim 11 wherein said drainage aid comprisesisodecyl alcohol ethoxylate.
 23. Method as recited in claim 17 whereinsaid drainage aid comprises 2-decylethoxy poly(ethyleneoxy) ethanol. 24.Method as recited in claim 11 wherein said drainage aid comprisesethoxylated 2-decanol.
 25. Method as recited in claim 11 wherein saiddrainage aid comprises ethoxylated aliphatic alcohol having a chainlength of about 12.2.